Export edited icons back into the native .icon package format

Editing an imported .icon and exporting it no longer collapses the icon into a single rendered image. The exporter writes the group and layer tree back out with each layer’s original artwork, plus its opacity, blend mode, visibility, and liquid glass settings (shadow, translucency, specular, blur) as real Icon Composer parameters.

A few things the format can’t represent — a group nested inside another group, an appearance override that has no Icon Composer equivalent, artwork that failed to decode — are called out as warnings after export rather than silently dropped.